The present invention relates to the field of electrical components and is to be applied in the construction of vacuum switching chambers whose housings have two cap-type metal parts and an annular insulator, and which are accordingly provided for switching applications in the low-voltage range.
In a conventional vacuum switching chamber described in German Patent No. 44 22 216 the two cap-type metal parts made of copper, one of which forms the actual switching chamber for a stationary and for an axially movable contact piece, are each connected in vacuum-tight fashion with the annular insulator at the end of the tube-shaped wall area, using a cutting soldering. In order to enable reliable switching of short-circuit currents in the range of 50 to 100 kA with this conventional vacuum switching chamber at the smallest possible axial and radial dimensions, the one end of the bellows in the immediate vicinity of the movable contact piece is soldered to the contact bolt thereof, and is concentrically surrounded by the annular insulator. A cap-type protective plate on: the base of the movable contact piece protects the bellows against electrical loading. This switching tube has no special shielding for the protection of the inner insulation path formed by the annular insulator, since a relatively broad end surface of the annular insulator faces away from the contact region. As is standard, the current terminals of this conventional vacuum switching chamber are constructed as bolts that are led axially through the respective cap-type metal part. In addition, the two contact pieces are constructed as cup-shaped (hollow) contacts, although other conventional contact shapes, are also possible. Another conventional contact shape described in European Patent No. 0 532 513, is offered for example by what are called spiral petal contacts, having in particular flat plate-type contact electrodes that are provided with slots that run from the outer circumference toward the inside. These slots can be made up of a straight section and a bored hole that penetrates the contact surface.
As a switching element for low-volt contactors, conventional vacuum switching tubes as described in German Patent No. 37 09 585 which forms a part of the outer surface of the housing, and is here on the one hand soldered in vacuum-tight fashion with the current terminal of the movable contact bolt and on the other hand is soldered in vacuum-tight fashion at the end side with a short tube-shaped insulator German Patent No. 195 10 850 describes that the bellows can be connected both with the insulator and also with the current terminal of the movable contact bolt, using a cutting soldering.
In addition, U.S. Pat. No. 4,555,007 describes that in vacuum switching tubes for medium-voltage applications, it is conventional to provide the shield surrounding the switching path with an intermediate layer made of the same material (CrCu alloy) of which the contact electrodes are made. In addition, as described in German Patent No. 29 44 286, for parallel operation of direct-current electrolytic cells, some conventional vacuum switches, given a switching voltage of approximately 4 volts, have to switch a current of approximately 4000 A, and in which the cylindrical contacts are provided with planar conductive end plates, in order to enable an electrical connection of the switch with electrical terminal rails.
An object of the present invention to further miniaturize the conventional vacuum switch chamber, at while same time increasing the switching capacity.
According to the present invention the current terminals of the two contact pieces are fashioned as plates that respectively form the base area of one of the two cap-type metal parts, also the bellows forms the wall area of the cap-type metal part that is allocated to the movable contact piece. Moreover a tube-shaped part, soldered at its end face with the plate-type current terminal of the stationary contact piece, forms the wall area of the other cap-type metal part.
Such a construction of the vacuum switching chamber leads to a flat construction, having a constructive length that is reduced significantly in comparison with conventional vacuum switching tubes. The construction of the current terminals in the form of plates, rather than the previously standard cylindrical bolts, contributes to this, these plates forming at the same time the end-face cover of the switching chamber, which in itself is cylindrical. The flat design of the new vacuum switching chamber can be even more clearly evident if the contact pieces are fashioned as spiral petal contacts, in particular as flat spiral petal contacts. In addition, the use of spiral petal contacts leads to better arc conducting, resulting in a better switching capacity. Thus, with the use of flat spiral petal contacts having a diameter of approximately 90 mm, short-circuit currents of up to about 130 kA can be switched. Independent of the diameter of the spiral petal contacts, it is advantageous to arrange a disc-shaped vapor seal(baffle) between the movable contact piece and the associated current-conducting bolt. This seal may be made for example of a chromium-nickel steel, and can be used, in vacuum switching, chambers having a small switching capacity, for the mechanical reinforcement of the movable spiral petal contact having reduced thickness.
The new construction of the vacuum switching chamber also enables an immediate binding of the stationary contact piece to the associated plate-type current terminal, as well as, for the movable contact piece, the use of a terminal bolt having a large diameter, ensuring an optimal heat dissipation. The compact overall design renders superfluous a special routing of the terminal bolt for the movable contact piece, as has previously been standard in vacuum switching tubes for power switches with the use of a plastic bushing. This enables a higher thermal loading of the vacuum switching chamber.
In addition, the new design of the vacuum switching chamber makes it possible to construct all the individual parts (except for the annular insulator) in self-centering fashion, so that all the individual parts can be soldered to one another in a single work pass (sealing soldering) without the use of expensive solder molds. For this purpose, it is advantageous for the stationary contact piece to be connected with the plate-type current terminal via a short centering support, and for the movable contact piece to be connected in centered fashion with the associated plate-type current terminal via a contact bolt.
The shape of the tubular part surrounding the two contact pieces, in particular the flat spiral petal contacts, depends on the switching capacity. Given a small switching capacity of approximately 40 to 60 kA, this part can be fashioned as a hollow cylinder. Given a larger switching capacity, i.e, given larger contact diameters, it is advantageous for the tube-shaped part to be provided with a conical taper at the end facing the annular insulator. This enables the use of an insulator and of a bellows having a diameter significantly smaller than that of the spiral petal contacts. Independent of the shaping of the tube-shaped part, which is may be made of copper, it is advantageous to provide this partxe2x80x94on the inner wall, in the area of the switching pathxe2x80x94with a lining (coating) that is arc-resistant, for example using sheet metal parts made of a chromium-copper compound material, or using a galvanic coating with chromium.